The present invention relates to a combustion control system and method for a direct-injection spark-ignition internal combustion engine and, more particularly, to a technique for controlling fuel injection timing and ignition timing of the engine in a cold start state where the early temperature rise (activation) of an exhaust catalytic converter is desired.
Japanese Patent No. 3325230 proposes, as a technique for activating an exhaust catalytic converter in a direct-injection spark-ignition internal combustion engine, performing split fuel injection during a time from an intake stroke to ignition timing in a state where the catalytic converter has not been warmed up to its activation temperature. More specifically, the split fuel injection of Japanese Patent No. 3325230 includes at least two fuel injection steps: an earlier injection step carried out during the intake stroke to form an uniform and lean air-fuel mixture in a combustion chamber of each engine cylinder and a later injection step carried out in the middle or late stage of a compression stroke, e.g., 45 crank angle degrees to crank angle degrees before compression top dead center to form an air-fuel mixture having a local unevenness of concentration in the combustion chamber in such a manner that the ignition of the later charge can initiate more complete combustion of the earlier charge by flame propagation. During the split fuel injection, the ignition timing is retarded by a predetermined amount from a MBT (minimum advance for best torque) point. The ignition timing is also set at a point before compression top dead center in a no-load engine operation range and at a point after compression top dead center in a low-speed, low-load engine operation range.